SUMMARY Glioblastoma (GBM) is the most common primary brain tumor in adults with a very poor prognosis. Given, the central role tumor resection plays in GBM therapy clinical care, understanding the specific influence of tumor resection on immune response in the tumor microenvironment offers a new platform for developing effective immune based therapies for GBM. We have recently developed syngeneic orthotopic mouse GBM-model of tumor resection and shown that tumor debulking results in substantial reduction of myeloid-derived suppressor cells (MDSCs) and simultaneous recruitment of CD4/CD8 T cells into the resection cavity. In this proposal, we will first generate GBM resection models from genetically distinct currently available mouse GBM lines and analyze profiles of immune cells infiltrated into tumor microenvironment pre- and post-tumor debulking. While resection of primary tumor has shown clinical benefit, systemically delivered or direct injection of therapeutic agents in tumor resection cavities has provided limited additional benefit. In our previous studies, we have extensively demonstrated that locally delivered receptor targeted engineered adult stem cells have therapeutic benefits and synthetic extracellular matrix (sECM) encapsulation of stem cells is necessary to prevent their rapid ?wash- out? post-transplantation in mouse GBM tumor resection cavity. In our recently published studies, we have shown that sECM encapsulated mesenchymal stem cell (MSC) mediated local delivery of bifunctional, immunomodulatory and cytotoxic protein, interferon (IFN) ? enhances selective post-surgical infiltration of CD8 T cells and directly induces cell-cycle arrest in tumor cells. However, IFN? has been known to upregulate program cell death ligand 1 (PD-L1) expression on tumor cells, thus hindering the immunomodulatory function of IFN?. Based on the recent findings that: blocking PD-L1 induced by IFN? treatment eradicates established tumors; tumor suppressor, phosphatase and tensin homolog (PTEN) loss promotes immune resistance; and our exciting preliminary data on: MSC-IFN? mediated upregulation of PD-L1 in vivo; and local delivery of ScFv-PDL1, we will create bimodal MSC expressing ScFv-PDL1 and IFN? and test them in syngeneic PTEN wild type (wt.) and mutant GBM models of resection. To ease clinical translation and ensure safety of our approach, we will ultimately engineer clinical grade human MSC to co-express ScFv-PDL1/IFN ? and HSV-thymidine kinase (TK) and test our approach in GBM tumors generated from patient derived GBM lines in humanized NSG mice. The incorporation of genetically engineered imaging markers markers into MSC and GBMs will allow us to follow MSC fate and efficacy in vivo and thus to fine tune the proposed approaches. The overall goal of this proposal is thus to immune profile genetically distinct GBM resection models and to assess rationale based therapeutic efficacy of immunomodulatory agents. Once validated, we will initiate a clinical study in which at the time of brain tumor surgery, the main tumor mass will be removed and encapsulated bimodal MSC will be introduced to enhance tumor cell eradication. This will have a major impact in saving the lives of brain cancer patients.